scalloped or cup tires

BMW Motorcycle tire scalloping and wear

by Duane Ausherman

This page applies to the front tire on solo bikes.  Tire cupping, or scalloping, is usually considered a sign of some problem.  The most blamed reason is out of balance.  Tire irregularities, loose steering head bearings, dings in the rim, and fork or frame alignment are also blamed.  None of that is true by itself.

Sidecar tires exhibit wear patterns, but nothing about a sidecar is symmetrical to start with, and the tread is harder for me to read.  This page is not about why the left side wears more in a country where we drive on the right-hand side.  You may read all about that aspect on this website.

Tire cupping is a sign of normal tire wear.  Chris (Native) just up and did these fine drawings and emailed them to me.  This is not the first time that he has fixed my poor artwork.  Many thanks to Chris.

This is supposed to be a side view of a typical front motorcycle tire under braking stresses.  See how the breaks in the tread get bent back from the traction? The trailing edge at B collapses into the empty area that is between the treads.  That edge wears little because it isn’t touching the road.  In a relaxed position, it shows up as a high spot.

The leading edge at A gets pulled back and wears off.  This part of the tread block becomes a low spot.

This view is supposed to be a straight-on view of a front motorcycle tire, under stress, from hard cornering.  Spot A, the outside of the tread block, collapses into the space and doesn’t wear down.  The part at B takes most of the wear and eventually shows up as “rounded off.”

This wear is normal for braking and leaning.  If you do little of either, then the wear will be far less.  The softer the tire compound, the greater the distortion from wear of this nature.  Racing soft and sticky tires get worn out in a few hundred miles.  Super hard road touring tires, gently ridden, can last 15 k miles.  A heavier bike that is ridden the same as a light one will “cup” more.  More tire air pressure will cause less cupping.

If two different riders rode two identical bikes, they probably would have different tire wear patterns. The one with more cupping would indicate that the rider rides the bike harder.

cup3.jpg (26530 bytes)

This photo shows a poor example of front tire wear.  Sorry, but I didn’t have a better example when I had my camera in hand.  Usually, a front tire will show more wear than this one.

Reading motorcycle front tire tread wear.

With this knowledge, one can “read” a tire.  More accurately, one can learn how the rider brakes and corners.  Leaning over will leave a high spot on the tread outside (away from the centerline of the tire).  Braking will leave a high spot at the rear of the tread, viewed as it touches the ground.  If one corners and brakes at the same time, the outside rear will have a high spot.

From examining the wear pattern, one may learn that the rider likes to lean one way more than the other.  The rider will also brake harder while leaning one way more than the other.  Compare the right side and left side wear.  The more worn, the more that the rider is comfortable in that lean.  Look at the rear of the tread block and see which side is more worn.  That is the side where the rider is more comfortable using the brakes.  Almost no rider is symmetrical in riding habits.  It is common to find braking wear on one side and cornering on the other.  The rider brakes before going into a right-hand turn and then goes through.  On left-hand turns, the rider is willing to apply brakes while in the turn.  Many combinations are possible.

This cupping wear pattern description applies to every tread block on the tire.  Sometimes one will find greater cupping at every third or fourth tread block.  This is evidence of a wheel that is out of balance.  Irregularly worn blocks are typical of an out-of-balance wheel.  Loose wheel bearings could also add to this odd wear.

Next time that you are around some motorcycles, try “reading” the tire wear.  Tell the rider which side is what and watch the surprised look.

The rear tire wear

The rear tire has quite different stresses on it; they are always more subtle and, therefore, harder to read.  The rear has both braking and acceleration stresses.  The wear from leaning is far less.  Since the front tire is on the same bike as the rear tire, I use the front for my “readings” of rider habits.

What can be done about it?

1.  A tire with a harder rubber compound will allow the tread to stay more rigid.  That will not permit as much cupping wear.  It also won’t safely allow as much hard cornering as a soft compound tire.

2.  Consider a tread pattern that is more angular and not as straight or square.

3.  Keep the inflation pressure up in the range that is specified by the manufacturer or higher.

4.  Don’t corner as hard.

5.  Don’t brake as hard.

Updated 13 July 2022